Fwiw, it's entirely possible for an airline to have a permanent voucher policy (and for it to make financial sense for them to do so). In the states, Southwest has always(?) had this on all their fares--even their lowest fares, not that there's much distinction between their fare types. In fact, during the beginning of the pandemic when carriers the world over were scrambling to adjust their marketing, IT, and retrain all their reps to allow for vouchers, Southwest slyly wrote on at least a couple ads something to the tune of, "We've always allowed 'free cancellation to a voucher' on any fare, so we have no new special policy to announce for the current situation."

It's an extremely customer friendly policy, but I'm quite certain they do it because it's a profitable stance for their business. Besides mollifying the concerns of worried customers (as several posters upthread have mentioned about what BwC has done for them towards BA) which presumably encourages more active booking, sometimes Southwest customers forget to cancel their ticket and the airline collects 100% of that money. I am convinced Southwest's actuarial/math/finance folk have integrated that into their profit models.

Of course, BA is a completely different bird... very different operation, stakeholders, customer demographic, etc. But just pointing out it can be done on even a large carrier. (Southwest sometimes likes to encourage the image that it's some kind of small provincial carrier, but in the peak of the pre-pandemic summer it does over 4000 flights a day lolol. Almost completely lower-48 domestic. And it doesn't have the kind of ten quid fares the ULCCs in Europe have which one might buy on a lark.)